Cold pressure gluing without retaining clamps



June 18, 1946. H. GALBER ETAL COLD PRESSUREYGLUING WITHOUT RETAINING CLAMPS Filed my 1s, 1944 2 Sheets-Sheet 1 gmc/www: Jiang @alb/er, y

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H. GALBER ETAL COLD PRESSURE GLUING WITHOUT RETAINING CLAMPS Filed May 15. 1944 June 18, 1946.

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Patented June 18, 1946 2,402,492 CULD PRESSURE GLUING WITHOUT RETAINING OLAMPS Harry Gelber and Alexander J. Golick, Seatt Wash., asignen to Wash.. a corporation 2 Claims.

This invention relates to an improved cold .pressure plywood gluing process and to press equipment for carrying out the process.

The cold process of gluing plywood. although partially replaced by recent developments of desirable hot press methods, is still extensively used. As at present practiced, the cold process requires considerable equipment auxiliary to the press and certain dimcultles in the product are occasioned by the very use oi this equipment. It is the object of the ,present invention to eliminate this auxiliary equipment, so greatly decreasing original plant costs and upkeep and greatly simplifying manipulative procedure, while at the same time, obtaining a superior product. In order that the accomplishment of the invention may be readily understood, we shall first oi all brieiiy describe the process heretofore used and point out the attendant disadvantages.

In prior practice, a heavy wooden press board, generally about three inches thick, is laid down adjacent the glue spreader and on top oi this board is generally laid a smoothly sanded plywood core board or caul about three-quarters of an inch thick. Six to eight inches in height of glued plies of dry veneer are then laid up on top of the core board followed by another threequarter inch core board, and so on until a pile oi a height of about four feet has been built up. This is capped by another three-quarter inch core board followed by another three inch press board.

In the press, platen pressure is transmitted to the press boards through top and bottom series of I beams whose ends project beyond the stack. As soon as the closing action of the .press has built up some pressure on the load, the press crew start placing turnbuckle clamps in position between the projecting ends of the upper and lower I beams. The turnbuekle clamps are made o! heavy metal and have fittings at each end which hook over the ends of the I beams, these fittings being connected by a, heavy turnbuckle. Each turnbuckle with its two clamping fittings weighs about twenty pounds. When the turnbuckles are tightened on the nnally compressed stack of plies, they and the I beams tend to maintain to a considerable degree the`pressure applied by the press. However, the actual degree to which the individual turnbuckles are tightened has been found by tests to vary widely the full pressure originally applied by the press platens maintained. With a crew oi two experienced men, clamping of the l. F. Laucks,

Inc., Seattle,

of Washington Application May 13, 1944, Serial No. 535,484

stack is completed clamp the stacks and return the heavy I beams and turnbuckle clamps to the press for use on other loads. A large stock of these clamps must be carried by a plywood mill, and, as they are heavy and specially made, this item alone often exceeds $10,000 for a single mill. The I beams add a considerable further expense. The heavy usage to which the clamps are subjected necessitates a very considerable maintenance cost for keeping them in first-rate operating condition so that they will work freely and be capable of rapid attachment and release.

Another item of expense is the cost and maintenance oi the heavy top and bottom press boards which have to be extremely strong and yet not too heavy for handling. They are usually glued up out of maple or nr stock to provide maximum stiffness and durability without excessive weight. Great stiiness is required because the I beams are spaced on about twelveinch centers and the press boards must be stiff enough to transmit the pressure satisfactorily not only to the areas in contact with each I beam but also as well as possibleover the intervening spaces.

In practice, the press boards are curved, marred and warped by the severe treatment to which they are subjected and a considerable maintenance and replacement item results. Furthermore, since the .press boards actually deflect inwardly slightly in the location of each I beam and swell outwardly slightly in the intervening areas, they fail to transmit uniform pressure to the assembled plies and this causes a definite and decidedly objectionable variation in local adheslon, particular in the top and bottom portions of the stack and, worse yet, cause these portions of the stack to be somewhat wavy instead of perfectly iiat. This waviness is a serious detriment to sanding the plywood panels, causing a certain amount of rejects and requiring a rather heavy cut to clear up the uneven surfaces.

Another objectionable feature, which hitherto has remained an unsolved problem, is that the system, on account of the crushing and deflect- 3 ingoithepressboardsaswellasthetailureo! the turnbuckle clamps'to apply fully adequate pressure, limits the application of gluing pressure to an amount which is deilnitely less than that which is ideal from a quality standpoint even if it were uniformly applied.. Thus. it can be seen that aside from the direct expense involved in the rst cost oi the I beams, turnbuckle clamps and press boards, and maintenance costs, the old system is inadequate from the standpoint of quality of product. The advantages of the hot press method have been recognized as arising in a considerable degree from the elimination oi these objectionable features of the cold press system. The present invention eliminates these disadvantages in a manner which will now be described with reference to the accompanying drawings in which,

Figure 1 is a plan view of a cold press instal1ation in accordance with the invention.

Figure 2 is an end elevation or the press which appears in Figure l, the press being open.

Figure 3 is a section on line 2-2 of Figure 2.

Figure 4 is a view, partly broken away, similar to that ot Figure 3, with the press closed, and

Figure 5 is a section on line 5 5 o1' Figure 3.

Referring to Figures l and 2, reference numeral I designates a glue spreader at one end oi' roller tracks Il and I2 whose other ends terminate on a supporting beam Il adjacent the press Il. Instead of using a heavy three-quarter inch caul, we start the stack on a thinner press board Il, Figure 3, and omit the caul entirely. The press board may be about two inches thick since in our process we discard the I beams and clamps altogether so that local pressures occasioned thereby are avoided. The bottom press board is placed across the tracks Il and I2 adjacent the glue spreader and the plywood stack is built thereon, using a three-quarter inch core board i' about every six or eight inches. and. nally. a cap constituted by another two inch press board Il, Figures 1 to 4. In the figures Just mentioned, it will be noted that a pair o! roller bars i1 and Il extend across and above the lower platen I9 in continuation oi tracks Il and I2 and are supported for free upward displacement at one end on the beam II and at the other end on a beam are disposed in continuation or the bars il and IB at the ends of the latter remote from the tracks Il and I2.

In accordance with the invention, we arrange on the platen i9 a rigid platform 2S which as here shown includes three solid blocks 2B, 21 and 2l having horizontal surfaces in a common plane which lies below the tops of the rollers as at 22. The blocks provide a continuous top surface except where they are spaced apart at 28 and 3|) to provide slots slightly wider than the roller bars Il and IB so that the latter can be freely received therein. The platform is fixed on the platen and is in e'ect a part thereof.

The plywood stack built up as above described is rolled into the press opening on the bars Il and II whereupon the lower platen is moved upwardly so that the top surface oi the platform 25 will engage the press board I6 and as pressure continues the press board i8 will be i'orced against the top platen 3i and eventually the roller bars will be engaged by the platen il and carried upwardly as indicated in Figure 4,

In the old practice, using Douglas fir, the total 4 pressure is relatively moderate and is equivalent to between the usual pressure range, we prefer to apply substantially higher pressure, close to the crushing strength of the wood, and, in the case of Douglas ilr plies, preferably inper square inch. The Dresi'or from about 5 to 25 miniactors which will be later the press.

In general summary, our improved cold process comprises cold pressing a stack ot glued plies with substantially uniformly distributed pressure over the top and bottom areas ot the stack, the pressure being of a magnitude and its interval of application being such that upon removing the pressure, the condition oi' adherence oi' the glued conned stack. the

died with safety.

While all of the dispersed uid glues ordinarily used in the cold process can be used in our modied process, we

provided by our process, and particularly our use of a much more uniform application oi' increased mechanical gluing pressure, permits corresponding modifications in the other gluing factors. We take adin the quality of the plywood. In cold process, the inability of the press boards to stand more than moderate local pressures is a bar to the use of the higher gluing pressures which we are able to employ. By using a somewhat heavier glue along with increased mechanical pressure. and in conjunction with the marked improvement in uniformity of pressure application which we obtain by eliminating the I beam clamps, we are able to produce decidedly more uniform adhesion with the same amount of glue required in the cold process hitherto used. If conditions require a high order of adhesion. we readily obtain it with a more generous spread, while, it a lower bond strength is permissible, we are able to reduce the spread oi glue and in either case produce a decidedly stronger and more uniform adhesion than has been obtained in the regular cold process hitherto.

In other words, our new process escapes the former necessity of wasting a certain amount of glue to overcome unavoidable lack of uniformity in the gluing conditions. In addition, we eliminate considerable labor formerly required to handlc the clamps and also eliminate their rst cost and maintenance as wel1 as most of the malntenance oi' the accessory heavy press boards. Our press boards are not only thinner but they last very much longer since they are neither deected nor crushed by excessive local pressures derived from the I beams and clamps.

Regarding the time which the load is maintained under pressure, this. of course, will vary according to the glue spread and other gluing conditions. A light spread on relatively thin plies and a moderate requirement for glue strength permits a very short pressing of only ilve minutes or a little more while a heavier spread and a speclcation calling for a high order of adhesion, as in thick plywood, will require a longer pressing time up to an extreme not ordinarily exceeding 25 minutes. In general, we find that satisfactory plywood can be made by our process with a pressing period of about l5 minutes. It will be seen that this is considerably longer than the press time of the old process but in many mills this does not prove a detriment since a considerable excess of press capacity is frequently available in mills using the regular cold press process. Also, on certain types of production, less press capacity is required. In a given press we avoid the loss of working space hitherto occasioned by the top I beams, the very thick press plates, and top and bottom cauls.

Aside from the many advantages which proceed directly from our main feature of elimihating the use of the cumbersome clamps, there are a number of minor advantages which, in the aggregate, are of considerable importance.

The low and irregular pressure application of the old cold process necessitates the use of a rather thin, sloppy glue to make it easier for the inadequate pressure to obtain contact between the surfaces to be adhered. In our process, this restriction is eliminated and we are able to slightly reduce the Water content and increase the viscosity of the glue which not only gives us a notably more uniform positive spread deposit but eliminates splashing during spreading and, in particular, reduces the wipes and displacement of glue during the handling of the plies.

As has been pointed out, our process permits us to use higher mechanical pressure on the plywood and to apply it more uniformly and to maintain it for a somewhat longer period. This is in conjunction with the use of a glue of somewhat higher viscosity, spread at a slightly reduced rate. These conditions combine to produce faster setting of the glue, better adhesion, and flatter panels. The faster setting is due to the slightly higher viscosity glue containing less water to get rid of. Also, the higher mechanical pressure causes the dry plies to illter ofi' the glue moisture more rapidly. The better adhesion is, of course, the combined result oi the more uniform deposit. the longer application of full pressure. and the better contacting of the surfaces to be adhered by the more complete smoothing out oi the superiiclal minute hills and valleys on the surfaces of the plies.

All oi this, oi course, improves the iiatness of the plywood since there are less irregularities in the local application of mechanical pressure, the glue water absorption is much more uniform and local areas oi' distortion and the local crushing of the plies caused in the old cold process by the deflection oi the press boards is also done away with. This improvement is immediately noticed by the sander operators in the plywood plants because it is no longer necessary to take heavy cuts to clean up the wavy panels formerly produced at and near the top and bottom oi the loads. Thus, not only is the general atness oi' the plywood improved, but the former causes for rejections of imperfect panels are also reduced. The cornbined effect of all these features is a substantial reduction in cost and improvement in quality It is most unexpected that a process of this nature should be found commercially practicable. particularly in view of the many years experience with the cold process clamping method. However, it has not hitherto been recognized that, if a relatively heavy, very uniform application oi pressure was continued on the plies for a sufiicient time and then they were left undisturbed for sev eral hours, the adsorptive character oi the dry veneer plus the filter press action obtained from the uniform pressure was capable of converting the adhesive into a strong enough gel to maintain the plies in contact during the remaining longer period required to dehydrate the glue substance to the point where its strength was suilicient to stand rough handling.

Variations in procedure and equipment are, of course, possible without departure from the i'ollowing claims. Among such variations, we refer, for example, to the use of non-pressure retaining clamps or carrying clamps which do not confine the stack to retain the pressure applied by the press but are merely convenient expedients which serve as slings for crane transportation of the stack from press to storage, For instance, some mills, in practicing the old cold process, have been accustomed to pick up the stacks and carry them to storage by using two of the pressure retaining clamps as convenient points oi attachment i'or the crane. By a slight modification, this convenient transportation method may still be used without departing from the principles of our invention as set forth in the following claims. It will be readily understood that, by providing two transverse charmels i'or I beams in both the top and bottom platens and inserting therein projecting I beams which substantially fill the slot openings and are the same height as the depth of these slots, the desirable continuous pressing surface is still provided and then the projecting ends of the I beams are available for connection with conventional turn-buckle clamps after the pressing and the clamps thus act as slings to afford secure points of attachment for the crane when the load is moved away to storage. It is pointed out that in such usage it would be impossible for two sets of clamps to retain the pressure or act as a pressure-applying continement for the stack. They could not be used for this purpose, even if it was desirable. because two clamps would then have to retain the pressure that in the old process is inadequately retained by three or four times that number. In the old cold process, where the clamps are properly tightened, breakage is frequent and. if the applied stresses were multiplied by three or four, breakage would be inevitable. Therefore. in the appended claims, it will be understood that, where we use the expression unconfined stack," we mean that the stack is unconiined as to the effective retention of pressing pressure and, where we use the expression "without resorting to the usual pressure retaining clamps." we do not exclude the use of such conveniences as carrying or crane attachment clamps since these are not pressure retaining clamps and could not peri'orm that function.

We claim:

l. The process of making plywood using a cold press and without resorting to the usual pressure retaining clamps, which comprises assembling a stack of dry porous veneer plies with a cold process viscous glue, cold processing the stack under substantially uniformly distributed pressure over substantially every point of the top and bottom areas thereof to initially convert the glue lm over its entire surface by the ilter press action of the adjacent dry porous plies into a strong enough gel to maintain the plies in contact upon removal of the pressure, the pressure being close to but not exceeding the crushing strength of the wood and its duration being in the range between about five and about twenty-five minutes, removing the pressure, and moving the released and unconflned stack en masse to another location and allowing it to stand undisturbed until the glue has set.

2. The process of making plywood using a cold press and without resorting to the usual pressure retaining clamps, which comprises assembling a stack of dry porous Douglas fir veneer plies with a cold process viscous glue, cold pressing the stack under substantially uniformly distributed pressure over substantially every point of the top and bottom areas thereof to initially convert the glue film over its entire surface by the filter press action of the adjacent dry porous plies into a strong enough gelt to maintain the plies in contact upon removal of the pressure, the pressure being between approximately i60 to 225 pounds per square inch and its duration being in the range between about five and about twenty-five minutes, removing the pressure, and moving the released and unconflned stack en masse to another location and allowing it to stand undisturbed until the glue has set.

HARRY GALBER. ALEXANDER J. GOLICK.

Certificate of Correction Patent No. 2,402,492.

June 18, 1946.

HARRY GALBER ET AL.

It is hereby certied that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 7, line 26, claim l, for processing read pressing; column 8, line 20, claim 2, for geit read gel; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 10th day of September, A. D. 1946.

[SEAL] LESLIE FRAZER,

First Assistant ommz'ssoner of Patents.

pressure or act as a pressure-applying continement for the stack. They could not be used for this purpose, even if it was desirable. because two clamps would then have to retain the pressure that in the old process is inadequately retained by three or four times that number. In the old cold process, where the clamps are properly tightened, breakage is frequent and. if the applied stresses were multiplied by three or four, breakage would be inevitable. Therefore. in the appended claims, it will be understood that, where we use the expression unconfined stack," we mean that the stack is unconiined as to the effective retention of pressing pressure and, where we use the expression "without resorting to the usual pressure retaining clamps." we do not exclude the use of such conveniences as carrying or crane attachment clamps since these are not pressure retaining clamps and could not peri'orm that function.

We claim:

l. The process of making plywood using a cold press and without resorting to the usual pressure retaining clamps, which comprises assembling a stack of dry porous veneer plies with a cold process viscous glue, cold processing the stack under substantially uniformly distributed pressure over substantially every point of the top and bottom areas thereof to initially convert the glue lm over its entire surface by the ilter press action of the adjacent dry porous plies into a strong enough gel to maintain the plies in contact upon removal of the pressure, the pressure being close to but not exceeding the crushing strength of the wood and its duration being in the range between about five and about twenty-five minutes, removing the pressure, and moving the released and unconflned stack en masse to another location and allowing it to stand undisturbed until the glue has set.

2. The process of making plywood using a cold press and without resorting to the usual pressure retaining clamps, which comprises assembling a stack of dry porous Douglas fir veneer plies with a cold process viscous glue, cold pressing the stack under substantially uniformly distributed pressure over substantially every point of the top and bottom areas thereof to initially convert the glue film over its entire surface by the filter press action of the adjacent dry porous plies into a strong enough gelt to maintain the plies in contact upon removal of the pressure, the pressure being between approximately i60 to 225 pounds per square inch and its duration being in the range between about five and about twenty-five minutes, removing the pressure, and moving the released and unconflned stack en masse to another location and allowing it to stand undisturbed until the glue has set.

HARRY GALBER. ALEXANDER J. GOLICK.

Certificate of Correction Patent No. 2,402,492.

June 18, 1946.

HARRY GALBER ET AL.

It is hereby certied that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 7, line 26, claim l, for processing read pressing; column 8, line 20, claim 2, for geit read gel; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 10th day of September, A. D. 1946.

[SEAL] LESLIE FRAZER,

First Assistant ommz'ssoner of Patents. 

